Injury (1990) 21,309-310 printed in Great Britain 309

Skin loss of the lower limb

D. S. Murray Wordsley Hospital, Stourbridge, West Midlands, UK

Introduction

This review article is short, incomplete and written by a plastic surgeon and, therefore, biased. No references are given but at the end of the paper are some suggestions for further reading. This paper only comments on post- traumatic skin loss and does not deal with skin loss caused by pressure sores, bums or the treatment of skin and subcutaneous tumours. The emphasis is on the initial treatment of lower limb skin loss.

Historical review

Until this century, skin loss of the lower limb with damage to underlying tissues, especially bone, frequently resulted in primary amputation. During the first 70 years of this century, the growth of reconstructive orthopaedic and plastic surgery stimulated efforts to repair skin loss of the leg, ankle and foot that were associated with underlying fractures or exposed joints and bone. Tube pedicles were brought down from abdomen to wrist and eventually to the leg; legs were crossed, immobilized and sutured together for weeks for cross-leg flap transfer and large jump flaps were transferred from abdomen to leg by a broad arm attachment. These were multistage techniques and although useful for secondary reconstruction of contractures, atrophic scars and covering non-infected exposed bone, they were of little use in the immediate reconstruction of skin loss.

There have been three important advances in the last 21 years in the treatment of severe open lower limb wounds. The first is the use of external fixators to control fractures. The second is the proper appreciation of the detailed vascular anatomy of the skin, fascia, muscle and bone of the lower limb, and the third has been the development and routine use of microsurgical techniques in the transfer of large pieces of vascular tissue for primary reconstruction of skin loss which cannot be grafted. However, the greatest advance, and one which must surely increase to be estab- lished as routine over the next 10 years, is that plastic surgeons and orthopaedic surgeons must co-operate from the beginning in the treatment of patients with severe lower limb skin loss.

When skin of the lower limb is lost and the base of the skin defect will not - or should not - take a skin graft, then flap cover is necessary. The flap brings its own blood supply to ensure viability and is usually thick to protect underlying vital structures. For years local flaps of skin and fat on the lower limb had a well-deserved reputation for unreliability resulting in frequent flap necrosis. Around 1970, Ponten, in Sweden, rediscovered the value of including the richly vascularized deep fascia when raising lower limb skin flaps. These fasciocutaneous flaps or ‘super’ flaps can be raised easily with predictable survival of flaps up to a length : breadth ratio of three : one.

At about the same time, the blood vessels to lower limb

0 1990 Butterworth-Heinemann Ltd 0020-1383/90/050309-2

muscles were precisely identified as to their number, course, direction, origin and importance. With this precise anato- mical information it was realized that some of these lower limb muscles could be freed from their origins, pedicled on one or more nutrient blood vessels and moved to cover local areas of skin loss. A split-skin graft was laid on the muscle. The skin above the superficial lower limb muscles is partially supplied by blood vessels arising from the main vessel to the underlying muscle. Thus a skin, fat and muscle flap (muscu- locutaneous or myocutaneous) can be used instead of a muscle flap with a split-skin graft. The most commonly used muscles for these flaps are the flexor hallucis brevis, gastrocnemius, soleus, rectus femoris, gracilis and tensor fasciae latae.

Sometimes, fasciocutaneous flaps, muscle flaps or myo- cutaneous flaps are not available, suitable or big enough to cover large skin defects. In such cases, microsurgical tech- niques are commonly used. Large pieces of tissue (muscle, fascia, skin and subcutaneous tissue) may separately or in combination be transferred from various parts of the body to the lower limb. These ‘free’ flaps have a predictably reliable constant vascular pedicle which can be anastomosed to a main lower limb artery and vein nearby. The ‘free’ flaps most commonly used in the lower limb are the latissimus dorsi muscle (with or without overlying skin) based on the thoracodorsal artery, the rectus abdominus muscle based on the inferior epigastric artery, the gracilis muscle based on its superior pedicle and the radial (fasciocutaneous) forearm flap based on the radial artery. Free flaps are particularly useful in reconstructing skin loss of the foot, ankle and lower two-thirds of the leg. The vascular anastomosis is usually performed by joining the end of the flap vessel to the side of the limb vessel and, therefore, not compromising limb vascularity. Occasionally, other tissues such as bone, tendon and nerve are incorporated into the flap for appropriate reconstruction. Free flap surgery needs initial specialized training, equipment, time and patience. It has an initial failure rate of up to 10 per cent, reducing to less than 4 per cent as experience and case selection is developed. Often, preopera- tive femoral angiography is needed to assess the status, position and number of arteries in the damaged limb. Patients must be fit enough for a long (3-6 h) operation.

Fortunately, flap cover of lower limb skin defects is only seldom needed. Split-skin grafts are sufficient if there is a vascular recipient bed and there are no vital exposed structures. The commonest cause of skin loss is the distally based pretibial traumatic skin flap, especially if it has been resutured back into place. Inevitably, at least one-third of the flap dies. These common injuries require thorough cleaning, haematoma removal, thinning of the non-bleeding distal part of the flap and replacement of the flap under no tension on its bed. The inevitable skin defect is covered by a perforated medium thickness split-skin graft. All this can be done under local anaesthesia, especially now that there is an efficient topical local anaesthetic cream available. Various

310 Injury: the British Journal of Accident Surgery (1990) Vol. 21/No. 5

regimens of delayed exposed grafting and immediate grafting with or without immobilization are practised and depend on the extent of skin loss and the physical and mental condition of the patient. Although skin grafting of lower limb skin defects is technically simpler than the use of flaps, expert care and attention to the wound is required in the first few postoperative weeks.

It is sometimes difficult to assess the extent of soft tissue damage immediately after injury, especially after crushing or degloving injuries. Fluorescein vital staining is helpful, but is difficult to judge and is not readily available. Careful clinical examination and removal of dead tissue will always be the basis of wound management. Although the edges of a wound may show dermal bleeding signifying viable skin, underlying muscle and fat may be dead or of dubious viability. It is essential to remove all dead soft tissue from and around the wound before reconstructing the defect or life-threatening infections may ensue. During this period of repeated examinations, the damaged area must be kept moist with a physiological solution.

Flap reconstruction of skin loss depends on the area of loss and its position.

Flap cover is rarely required for skin loss of the groin and thigh due to muscle covering the femur and the main neurovascular bundle. If required, muscle and musculocu- taneous flaps of rectus femoris, gracilis, sartorius, tensor fasciae latae and rectus abdominis are readily available.

Around the knee and upper third of the tibia there are many flap options. Fasciocutaneous flaps based proximally on the thigh and side of the knee and extending down the medial and lateral sides of the leg can be elevated and transposed into the skin defect. The flap donor site is skin grafted and this leaves a cosmetic defect but little functional loss. Through appropriate vertical access incisions, the medial and/or lateral heads of gastrocnemius can be freed from their attachments, placed over the area of skin loss and the muscle bellies grafted. Overlying skin on the gastro- cnemius can be taken with the muscle but leaves an obvious contour defect. Free muscle or fasciocutaneous flaps are used for large defects, with the flap vessels anastomosed to the femoral or popliteal vessels.

Skin loss of the ankle and lower two-thirds of the leg is often associated with bone, joint and muscle damage. The soleus muscle flap can be used for small- to medium-sized defects in the middle third of the leg. Elsewhere, if fasciocutaneous flaps cannot be used then a free flap is needed. If there is an open fracture with skin loss, then initial treatment by a combined plastic surgical and orthopaedic approach as previously detailed is ideal. The latissimus dorsi free muscle flap is commonly used - its long vascular pedicle enables the microsurgical anastomosis to be performed on the leg vessels (usually the posterior tibial) above the zone of injury. The papers by Godina and Yaremchuck should be read by all involved in this field.

Because of the peculiar and specialized nature of foot skin, a small area of loss of the full thickness of the weight-bearing sole skin can lead to difficulty in walking - a difficulty made much worse if there is underlying damage to bone or joint. There is, however, a rich blood supply in the healthy foot with good communications between terminal branches of the anterior and posterior tibial arteries. Thus, many flaps can be designed on the sole for transposition or rotation anteriorly or posteriorly. These flaps may be fascio- cutaneous or musculocutaneous (based on the flexor hallucis brevis and adductor digiti minimi). They can cover most of the weight-bearing areas of the foot by using instep skin. If a

large area of sole skin is lost, then a thick, split-skin graft, or if necessary, a thinned-out free muscle flap which is contoured to the foot and covered with a split-skin graft, is used. As important as the surgery is the education of the patient to look after his insensible feet so that plantar skin ulceration is reduced.

Skin loss on the dorsum of the foot can usually be corrected by skin grafts. Exposed viable tendons and open joints require flap coverage, and here the free radial forearm flap is particularly useful. Filleting toes and using the toe skin envelope still remains a reasonable and quick method of covering areas of small skin loss adjacent to toe bases.

A frequent difficulty in the ‘healed’ injured lower limb is the persistence of an atrophic, tight, adherent scar tethered to bone and often surrounded by discoloured, poor quality skin. This scar is vulnerable, often repeatedly breaks down, may lead to an osteomyelitis, and, if left for many years, may undergo malignant change. Treatment entails excising the scar and surrounding abnormal skin and covering the defect with flaps as described above. However, in these recon- structions of ‘secondary’ skin loss, many new local lower limb flaps designed on a distal pedicle have been used. They are usually fasciocutaneous in nature and based on known perforating vessels. They are not commonly used flaps and are of little use for primary skin loss, but they are very useful in secondary reconstruction, especially in the lower third of the leg.

Chronic, post-traumatic osteomyelitis of the tibia is often associated with either overlying skin loss or poor quality skin. In the treatment of this condition, after the affected bone and associated tissues have been removed, a muscle flap, either pedicled or free, should be introduced to fill the cavity and, if necessary, be a base for skin grafts for skin cover. This muscle flap contributes greatly to healing of this difficult wound and is an ideal conduit for delivery of antibiotics.

During the 21 years that Injury has been published, the management of severe skin loss of the lower limb has improved dramatically due to new techniques in plastic and orthopaedic surgery. Hopefully, in 21 years from now, major lower limb injuries involving skin loss will automati- cally be treated from the onset by a combined plastic and orthopaedic approach. Sadly, today, there is insufficient cooperation between the two surgical disciplines in the treatment of these patients.

Suggested further reading

Cormack and Lamberty (1987) The Arferiul Anatomy of Skin Flaps. London and Edinburgh: Churchill Livingstone.

Mathes S. J. and Nahal F. (1982) Clinical Applications for Mud and Musculomfaneow Flaps. St Louis: C. V. Mosby.

Ponten B. (1981) The fasciocutaneous flap; its use in soft tissue defects of the lower leg. Br. 1, Hasf. Surg. 34,215.

Yaremchuck M. J., Brumback R. J., Manson P. N. et al. (1987) Acute and definitive reconstruction of osteocutaneous defects of the lower extremity. Pkwf. Reconsfr. Surg. 80, 1.

Godina M. (1985) Early microsurgical reconstruction of complex trauma of the extremities. Plasf. Reconsfr. Surg. 78,2.

Requesfs for reprints shouti be acUres.& to: Mr D. S. Murray FRCS,

Consultant Plastic Surgeon, Wordsley Hospital, Nr Stourbridge, West Midlands, UK.